I'm self-learning a bit about preferred fits and tolerances and was wondering why transition fits were even a thing.
Clearance fits I understand, applications where you don't want parts to touch and "clear" each other.
Interference fits are for snug, more rigid connections which require pressing.
However, why would you want a transition fit which sometimes is clearance, and sometimes is interference? Doesn't that make your end product variable and not consistent?
A transition fit actually makes the end product more consistent than the clearance fit. In transition fit clearance (if occurring) is less compared to the clearance fit. Also, if interference occurs, we don't need to used press fit or temperature based shrink fit. We can simply use mallet for transition fit. This makes transition fit a preferable choice in case of the higher quality grade equipment such as Gears (cycloidal), Hubs, driven bushes where more accuracy is needed.
Transition fit is mostly used for accurate location, a compromise between clearance and interference.
For example consider two gears with cycloidal profile where you need the center distance between the shafts to be exact or with the maximum accuracy. Here, a clearance fit my cause less accuracy resulting in more vibrations in cycloidal gears. While the interference fit my cause the replacement of the gear difficult as shaft can be damaged while replacing the gear. Here a compromise is made between clearance fit and interference fit.
Can't transistion fits also be called out when you're manufacturing a lot of mating parts (thinking 2-liter bottles and their caps or big box stores that sell furniture that will be assembled at home by the customer) and use sorting machines to sort the parts (small, medium, large, etc.) to get really tight fits between parts that were made with loose tolerances (i.e. cheap)?
